10.23.2018
Experiment leaders: Hannah Seo and Ashish Jayaraman
This experiment constituted our first visit to the Murray Middle School, St. Paul, MN. We were hosted by Ms. Nix and our group included students from grades 7 and 8 in their Astronomy class. We visited twice in the week as indicated by the dates with 36 and 24 students respectively on Tuesday and Wednesday. The classroom contained single desk-chair arrangements for lecture as well as six lab benches for experiments including a water faucet.
We chose the experiment based on the general theme of the Astronomy class trying to answer the following questions: 1. Why is the sky blue and why does it change with the time of the day? 2. How will the sun look if the earth’s atmosphere, instead of being a concoction of gases and particulates, was actually colored?
We started the class time with a short presentation introducing the mentors. We also discussed how the mentors use the scientific method as graduate student researchers and how we will be using the scientific method in the experiments we conduct during our visits to the school. Then we moved on to a presentation with background information the students needed to perform the experiment. First, we demonstrated the constituents of sunlight and demonstrated the splitting of white light through a prism to show the seven different colors that make up sunlight. We then asked the students about why different objects were seen to have different colors. We followed that up with telling them about the atmosphere and how it scatters light that comes from the sun. We hinted to them about how the extent of scattering is a function of the distance through which the light is scattered.
Experimental details:
Part 1: The first part of the experiment aimed to have the students understand why the sky is blue and how the color is different depending on the time of the day.
The students made translucent solutions of milk powder in water (~100 mg/L) in glass vessels of three different diameters as a proxy for three different scattering distances. They then took turns in shining white light from a flashlight through the different solutions and observed the color of the scattered beam from the top and the transmitted light on a white screen. In all three cases, the vessels looked blue when looked at from the top and the color of the beam on the white screen went from being white to yellow with increasing diameter of the vessel i.e. increasing scattering distances. We then simulated ‘fog’ by doubling the concentration of milk powder leading to a drastic reduction in intensity of yellow color on the screen in all three cases. The students noted the color they observed on the screen as the function of the diameter of the vessel.
Part 2: Colored light through colored solutions
The students added food coloring (red, green, blue, yellow) into the water with and without milk powder. They used lights of different colors (red, green, blue) and observed the color of the light on the screen as a function of the food coloring. The students were amazed by how choosing different combinations leads to different effective colors of the solutions based on the mixing of colors. The students had a lot of fun mixing the colors and trying out various combinations of the lights.
Part 3: Demonstration of total internal reflection (TIR)
As an aside, some mentors demonstrated TIR to their groups. The experiment involved looking at the path of a laser light incident on the air-water interface in a vessel. Milk powder was used to make the path of the beam apparent. It was shown that changing the angle of incidence allowed different extents of the laser to be reflected from the air-water interface and be obtained on a white screen set on the benchtop. The students were amazed by how the air-water interface acted like a mirror and were encouraged to think about why the sun is visible after it has passed the horizon during sunset and why the mast of a ship is visible for much longer after the ship has left the line of sight of an observer on the shore.
The first visit to Murray was quite a blast with the students and the teacher excited about the experiments. A majority of the class was engaging during the presentation and even more so while doing the experiments. We mentors are also equally excited to be back and show them the beauty of the scientific method and help them appreciate science as an avenue to understand the ‘magic’ happening around us every day.